U.S. patent number 7,662,205 [Application Number 11/371,238] was granted by the patent office on 2010-02-16 for processes to beneficiate heat-dried biosolid pellets.
This patent grant is currently assigned to Vitag Corporation. Invention is credited to Jeffrey C. Burnham.
United States Patent |
7,662,205 |
Burnham |
February 16, 2010 |
**Please see images for:
( Certificate of Correction ) ** |
Processes to beneficiate heat-dried biosolid pellets
Abstract
This invention is directed to systems, devices and methods for
modifying the process of producing dried biosolids pellets or
granules into beneficiated inorganically-augmented bioorganic
fertilizer. The present invention describes a method to beneficiate
heat-dried biosolids or sludge pellets or granules as presently
manufactured by municipalities or companies from a) dewatered
municipal wastewater biosolids or sludges within the municipal
wastewater treatment plant heat-dried biosolids production facility
or from b) finished dry heat dried biosolids pellets or granules in
a separate manufacturing facility from the municipal wastewater
treatment plant to produce a fertilizer containing sufficient
organic and inorganic plant nutrients to be valuable and saleable
into the commercial agricultural industry. The present invention
describes beneficiation methods to increase the plant nutrient
content to a level which permits the finished beneficiated dried
biosolids pellet or granule product to compete in the commercial
agricultural fertilizer marketplace and also to reduce the odors
associated with traditionally-produced heat dried biosolids.
Inventors: |
Burnham; Jeffrey C. (Aiken,
SC) |
Assignee: |
Vitag Corporation (Beech
Island, SC)
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Family
ID: |
37417785 |
Appl.
No.: |
11/371,238 |
Filed: |
March 9, 2006 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20060254331 A1 |
Nov 16, 2006 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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60659434 |
Mar 9, 2005 |
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60700730 |
Jul 20, 2005 |
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Current U.S.
Class: |
71/11; 71/64.03;
71/25; 71/22; 71/21; 71/17; 71/15; 71/14; 71/13; 71/12 |
Current CPC
Class: |
C05C
3/00 (20130101); C05F 7/00 (20130101); C05C
3/00 (20130101); C05D 3/02 (20130101); C05F
3/00 (20130101); C05F 7/00 (20130101); Y02A
40/213 (20180101); Y02A 40/20 (20180101) |
Current International
Class: |
C05F
3/00 (20060101); C05F 11/00 (20060101); C05F
7/00 (20060101); C05F 9/00 (20060101) |
Field of
Search: |
;71/11-27,64.03 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0143392 |
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Jun 1985 |
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EP |
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0557078 |
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Aug 1993 |
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EP |
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2133115 |
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Nov 1972 |
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FR |
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2757504 |
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Jun 1998 |
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FR |
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58032638 |
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Feb 1983 |
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JP |
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Primary Examiner: Langel; Wayne
Attorney, Agent or Firm: Remenick PLLC
Parent Case Text
REFERENCE TO RELATED APPLICATIONS
This invention claims priority to U.S. Provisional Application No.
60/659,434, entitled "Processes to Beneficiate Heat-Dried Biosolid
Pellets," filed Mar. 9, 2005; and U.S. Provisional Application No.
60/700,730, entitled "Process to Increase Plant Nutrient Content in
Heat-Dried Organic-Based Sludges," filed Jul. 20, 2005, which are
both specifically and entirely incorporated by reference.
Claims
The invention claimed is:
1. A method for the manufacture of a fertilizer comprising: mixing
dewatered biosolids, an oxidant, and a concentrated acid to form a
thixotropic mixture; subjecting the thixotropic mixture to a
pressure exceeding atmospheric pressure; adjusting the pH of the
thixotropic mixture to a pH of between pH 4.5 and pH 7.0; mixing
granulating agents into the mixture; and drying the mixture to
greater than 90% solids to produce a beneficiated, dried-biosolids
fertilizer.
2. The method of claim 1, wherein the oxidant is selected from the
group consisting of ferrates, chlorine dioxide, hydrogen peroxide,
oxygen, ozone and combinations thereof.
3. The method of claim 1, wherein the beneficiated, dried-biosolids
fertilizer has an inorganic plant nutrient value of 8% to 22%
nitrogen.
4. The method of claim 1, wherein the beneficiated, dried-biosolids
fertilizer has little to no detectable odor as compared to the
dewatered biosolids.
5. The method of claim 1, further comprising adding an inorganic
plant nutrient to the thixotropic mixture.
6. The method of claim 5, wherein the inorganic plant nutrient is
selected from the group consisting of solid fertilizers, iron,
nitrogen, potassium, sulfur, ammonium salts, ammonium sulfate,
ammonium nitrate, mono-ammonium phosphate, di-ammonium phosphate,
potash, urea, methylene urea, sulfur-coated urea, liquid
fertilizers, urea ammonium nitrate ("UAN"), liquid urea, liquid
N-P-K fertilizers 16-4-8, 10-8-8 or 6-14-6, and combinations
thereof.
7. The method of claim 1, further comprising adding a hardener to
the thixotropic mixture.
8. The method of claim 1, further comprising forming pellets or
granules.
9. The method of claim 8, wherein the pellets or granules are
coated with an agent to reduce dust and abrasion.
10. The method of claim 9, wherein the coated pellets or granules
are cooled to less than 55.degree. C.
11. The method of claim 1, which is conducted entirely within a
single heat-drying facility.
12. The method of claim 1, further comprising adding a chemical
additive directly to the dewatered biosolids to produce a
thixotropic mixture prior to drying.
13. The method of claim 12, wherein the chemical additive is added
to the dewatered biosolids without making a slurry.
14. The method of claim 1, wherein the concentrated acid reacts
with aqueous or anhydrous ammonia to produce ammonium salts.
15. The method of claim 14, wherein the concentrated acid is
phosphoric acid, sulfuric acid, or both.
16. The method of claim 1, further comprising adding a plant
nutrient to the mix to enhance fertilizer value.
17. A method for the manufacture of a fertilizer comprising: mixing
dried biosolids, an oxidant, and a concentrated acid to form a
thixotropic mixture; subjecting the thixotropic mixture to a
pressure exceeding atmospheric pressure; adjusting the pH of the
thixotropic mixture to a pH of between pH 4.5 and pH 7.0 by adding
an inorganic plant nutrient; and producing a beneficiated,
dried-biosolids fertilizer.
18. The method of claim 17, wherein the dried biosolids are greater
than 90% solids.
19. The method of claim 17, wherein the dried biosolids comprise
pellets or granules.
20. The method of claim 17, wherein the oxidant is selected from
the group consisting of ferrates, chlorine dioxide, hydrogen
peroxide, oxygen, ozone and combinations thereof.
21. The method of claim 17, wherein the beneficiated,
dried-biosolids fertilizer has an inorganic plant nutrient value of
8% to 22% nitrogen.
22. The method of claim 17, wherein the beneficiated,
dried-biosolids fertilizer has little to no detectable odor as
compared to the dewatered biosolids.
23. The method of claim 17, wherein the inorganic plant nutrient is
selected from the group consisting of solid fertilizers, iron,
nitrogen, potassium, sulfur, ammonium salts, ammonium sulfate,
ammonium nitrate, mono-ammonium phosphate, di-ammonium phosphate,
potash, urea, methylene urea, sulfur-coated urea, liquid
fertilizers, urea ammonium nitrate ("UAN"), liquid urea, liquid
N-P-K fertilizers 16-4-8, 10-8-8 or 6-14-6, and combinations
thereof.
24. The method of claim 17, further comprising adding a hardener or
granulating agent to the thixotropic mixture.
25. The method of claim 17, further comprising cooling the dried
mixture to less than 55.degree. C.
26. The method of claim 17, wherein manufacture of the dried
biosolids takes place independently of the manufacture of the
beneficiated, dried biosolids fertilizer.
27. The method of claim 17, wherein manufacture of the dried
biosolids takes place in a different facility than the facility
where the beneficiated, dried biosolids fertilizer is
manufactured.
28. The method claim 17, wherein the manufacture of the
beneficiated, dried-biosolids fertilizer avoids transportation of
untreated biosolids from a wastewater treatment plant.
29. The method of claim 17, wherein the concentrated acid reacts
with aqueous or anhydrous ammonia to produce ammonium salts.
30. The method of claim 17, wherein the concentrated acid is
phosphoric acid, sulfuric acid, or both.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention is directed to systems, devices and methods for
modifying the process of producing dried biosolids pellets or
granules, or manure or animal residual pellets or granules, or
other organic materials, such as food or pharmaceutical
fermentation residuals, formed into pellets or granules into
beneficiated inorganically-augmented bioorganic fertilizer. The
present invention describes a method to beneficiate heat-dried
biosolids or sludge pellets or granules as presently manufactured
by municipalities or companies from dewatered municipal wastewater
biosolids or sludges to produce a fertilizer containing sufficient
organic and inorganic plant nutrients to be valuable and saleable
into the commercial agricultural industry.
2. Description of the Background
The disposal of sludges discharged from large-scale wastewater
treatment plants is a serious and growing problem. In 1990, the
United States Environmental Protection Agency indicated that a
family of four discharged 300 to 400 gallons of wastewater per day.
From this wastewater, publicly owned treatment works generated
approximately 7.7 million dry metric tons of sludge annually or
about 64 dry pounds of sludge for every individual in the United
States. By the year 2000, these figures had doubled.
The definitions of "sewage sludge" and "sludge" under by Title 40
of the Code of Federal Regulations, Part 257.2, hereby incorporated
by reference, is as follows: "Sewage sludge means solid,
semi-solid, or liquid residue generated during the treatment of
domestic sewage in a treatment works. Sewage sludge includes, but
is not limited to, domestic septage; scum or solid removed in
primary, secondary or advanced wastewater treatment processes; and
a material derived from sewage sludge. Sewage sludge does not
include ash generated during the firing of sewage sludge in a
sewage sludge incinerator or grit and screenings generated during
preliminary treatment of domestic sewage in a treatment works.
Sludge means solid, semi-solid or liquid waste generated from
municipal, commercial, or industrial wastewater treatment plant,
water supply treatment plant, or air pollution control facility or
any other such waste having similar characteristics and
effect."
There are several types of sludges that can be produced by sewage
and/or wastewater treatment. These include primary sludge, waste
activated sludge, pasteurized sludge, heat-treated sludge, and
aerobically or anaerobically digested sludge, and combinations of
all. These sludges may be from municipal and/or industrial
sources.
Most commonly, sludges are dewatered to the best extent possible by
chemical and mechanical means. The water content of sewage sludges
is still very high. Typical sludges coming out of a gravity
clarifier may have a dry solids content of 2% or less. After
anaerobic digestion, the solids content can be about 10%. Cationic
water-soluble polymers have been found useful for causing further
separation between the solids and the water that is chemically and
physically bound. Filtration or centrifugation of cationic polymer
treated sludge typically yields a paste-like sludge cake containing
about 20% solids.
Drying of sewage sludge has been practiced for many years in both
the United States and Europe. Sludge drying in the United States
prior to about 1965 was undertaken to reduce transportation costs
and in pursuit of various disposal options. In some plants, the
sludge was dried in powder form and the fine particles were
consumed in the combustion chamber of an incinerator or boiler. In
the late 1960's two municipalities, Houston and Milwaukee, began to
market a pelletized or granulated dried sludge for use as a soil
amendment and/or fertilizer. Several more plants for manufacture of
dried pelletized sludge were built in the 1980's and 1990's;
especially after ocean dumping of sludge by coastal cities was
eliminated. Drying and conversion to a pelletized fertilizer was
the best option for these metropolitan areas where landfills and
land for disposal were limited. However, the investment required
for a sludge drying facility is large. A typical unit costs about
$150 million for equipment alone.
The most common type of sludge dried and pelletized is
anaerobically digested municipal sewage. Anaerobic digestions, as
the name suggests, involves treatment by facultative bacteria under
anaerobic conditions to decompose the organic matter in the sludge.
After a prescribed time and temperature, a sludge relatively free
of putrifiable organic matter and pathogens is obtained. Municipal
anaerobically digested sewage sludge is therefore preferred for
agricultural purposes.
However, dry sewage sludge has several disadvantages for
agricultural use. It has low fertilization value, typically having
nitrogen content of only about 2-5%. Freight and application costs
per unit of nitrogen are high. It often has a disagreeable odor,
particularly when moist. It has low density and when blended with
other commercial fertilizer materials, it may segregate into piles
or may not spread on the field uniformly with other more dense
ingredients. Bacterial action may continue and under storage
conditions sludge temperature may rise to the point of
autoignition. Hence, except for special markets that value its
organic content for soil amendment or filler in blended fertilizer,
there is little demand for the product. In most cases
municipalities must pay freight charges, or may offer other
incentives for commercial growers to use the material. However,
this is frequently still more economical than alternative disposal
schemes.
The market value for fertilizers is principally based on their
nitrogen content. A need exists for a practical and economic method
for increasing the nitrogen content of sewage sludge to a level
approaching that of commercial mineral fertilizers, i.e., 10-20%.
Freight costs and the cost of application per unit of nitrogen
would then be much lower. Overall value and demand would increase.
Moreover, sludge has an advantage in that its nitrogen is of the
slow release type. The nitrogen is part of organic molecules and
hence is available to growing plants only when the molecule is
broken down. This is very desirable since it provides nitrogen to
the plant all through its growing cycle. Manufactured slow release
nitrogen fertilizers have a price nearly 10 times that of ordinary
mineral nitrogen fertilizers. Conceivably, municipalities would
enjoy a credit rather than an expense in disposing of their dried
sludge product if the total nitrogen content can be increased and
the tendency for autoignition reduced or eliminated.
Prior attempts have been made to reach some of these objectives.
U.S. Pat. Nos. 3,942,970, 3,655,395, 3,939,280, 4,304,588, and
4,519,831 describe processes for converting sewage sludge to
fertilizer. In each of these processes a urea-formaldehyde
condensation product is formed in situ with the sludge. However,
the processes require the handling of formaldehyde, a highly toxic
lachrymator and cancer suspect agent.
French Patent No. 2,757,504 describes the blending of mineral
fertilizers with organic sludge. The mixture is heated to a
temperature between 200.degree. C. and 380.degree. C. Japanese
Patent No. 58032638 describes a process where sludge is treated
with sulfuric and nitric acids or sulfuric and phosphoric acids and
ammonia under elevated pressure of about 3 atmospheres. These prior
art processes require costly process equipment and/or special
conditions not readily incorporated in existing sewage treatment
facilities.
The simplest method of increasing the nitrogen in sludge would be
to add commercial nitrogen fertilizer materials to the wet sludge
prior to drying and pelletizing. There are only a few high-nitrogen
fertilizer materials that are economic for use in agriculture:
ammonia (82 wt. % N), urea (37 wt. % N), and ammonium nitrate (35
wt. % N). Ammonia has high volatility and is subject to strict
regulation of discharges to the atmosphere. Urea is a solid that
adsorbs moisture quite readily and makes the sludge more difficult
to dry. It is also highly susceptible to breakdown to ammonia by
the microbes and enzymes in sludge, resulting in nitrogen loss and
an odor problem. Ammonium nitrate is a strong oxidizer and creates
a potential explosion problem. All of these fertilizers have high
nitrogen content: but are unsuitable for combining with sludge.
Another possible candidate that has been unsuccessfully tested by
the industry as an additive to sludge is ammonium sulfate. Although
ammonium sulfate has lower nitrogen content (21 wt % N) than the
materials discussed above, it has a price per unit of nitrogen
comparable to that of the other commercial fertilizers. It is also
relatively inert to the microbes and enzymes in sludge.
It has been found in full-scale plant trials that a problem occurs
during the drying of a mixture of ammonium sulfate and sludge.
Title 40 of the Code of Federal Regulations, Part 503, Appendix B
specifies that the temperature of the sewage sludge particles must
exceed 80.degree. C. (176.degree. F.) or the wet bulb temperature
of the gas in contact with the sewage sludge must leave the dryer
at a temperature exceeding 80.degree. C. (176.degree. F.). However,
when drying a mixture of ammonium sulfate and sludge, a sudden
release of ammonia vapors occurs at about 60.degree. C.
(140.degree. F.) overwhelming the air pollution control system.
Several attempts at addition of ammonium sulfate to sewage sludge
in several different plants over several years have foundered on
this problem. The discharge of ammonia to the atmosphere is
environmentally intolerable. Consequently, ammonium sulfate
addition to sewage sludge has not been successful to date.
European Patent No. 0143392 B1 describes a process in which an
undigested liquid sludge is mixed with salts such as ammonium
sulfate at a concentration of 17-47 wt. % at a pH of 2-6 for a
period of 3 to 12 hours followed by disposal. Japanese Patent No.
9110570 A2 describes the treatment of sewage sludge with an acidic
solution followed by drying to reduce ammonia evolution and to
retain the effective nitrogen. Therein is described the use of
dilute (0.3 Normal) aqueous solutions of HCl, H.sub.2SO.sub.4, and
wood vinegar as ammonia binders ("Granulation of Compost From
Sewage Sludge. V. Reduction of Ammonia Emission From Drying
Process", Hokkaidoritsu Kogyo Shikenjo Hokoku, 287, 85-89 (1988)).
None of these references disclose the use of acids with ammonium
sulfate additions and neither reference discusses the issue of
corrosion of steel process equipment under acid conditions.
Over the past thirty years alkaline stabilization of sludges has
been a standard and successful method of making sludges into
beneficially useful materials that can be used principally as
soil-conditioning materials. Because these sludges have high
calcium carbonate equivalencies, they have been produced and
marketed as AG-lime materials, usually as a replacement for calcium
carbonate in farm soil management strategies. Because of this usage
the value of these materials has been restricted to only a few
dollars per ton of product, they are economically and
geographically restricted because of transportation costs to areas
close to the source of their treatment. Many of these
alkaline-stabilized sludges contain up to 65% water.
Thus, there is a long standing need for practical means of
increasing the economic value of sewage sludge through increasing
its nitrogen content, and increasing its ability to be spread as
well as a need to treat these materials such that they are
converted into commodity fertilizers with physical and chemical and
nutrient properties such that they can command significant value in
the national and international commodity fertilizer marketplace.
The present invention meets those needs.
SUMMARY OF THE INVENTION
The invention overcomes the problems and disadvantages associated
with current systems and methods of manufacturing fertilizers from
sludge and related waste materials, and also the fertilizers
prepared by these methods.
One embodiment of the invention is directed to a method for the
manufacture of a fertilizer comprising mixing an oxidant to
Another embodiment of the invention is directed to
Other embodiments and advantages of the invention are set forth in
part in the description, which follows, and in part, may be obvious
from this description, or may be learned from the practice of the
invention.
DESCRIPTION OF THE FIGURES
FIG. 1 Municipal Wastewater Treatment Plant Schematic Illustrating
Three Beneficiation Treatment Input Sites.
FIG. 2 The PB or Pellet Beneficiation Process Preferred
Embodiment.
FIG. 3 The Pellet Beneficiation Process.
FIG. 4 The Bio-Tablet or Bio-Extrusion Pellet Beneficiation
Process.
FIG. 5 The PB Bio-Extrusion Fertilizer Process Schematic.
FIG. 6 Pellet Beneficiation Process for Wastewater Treatment
Plants.
DESCRIPTION OF THE INVENTION
The present invention creates an inorganically-enhanced bioorganic
fertilizer by modifying the biosolids heat-drying pellet or granule
(hereafter referred to as "pellet" or "pellets") manufacturing
processes presently used by many U.S. and worldwide municipal
wastewater treatment plants. In addition, the present invention
teaches treatment of sludges or biosolids to reduce noxious
odorants prior to the drying step or steps in the manufacture of
heat dried pellets and further teaches the addition of specific
chemicals such as one or more oxidants selected from the group
comprised of iron oxides such as ferrates, other metal oxides,
oxygen, hydrogen peroxide, other peroxides, ozone and chlorine
dioxide to further reduce odors. The present invention teaches that
the use of these methods individually and more importantly in
combination creates a beneficiated heat dried pellet. In the art,
beneficiated is known as inorganically-augmented.
The fertilizer dried pellet created by the present invention can be
chemically adjusted to fit the needs of nitrogen, phosphorus and/or
potassium fertilizer requirements by containing significant amounts
of nitrogen, phosphate and other plant nutrients like potassium,
sulfur and/or calcium to: a) enhance commercial valuation, b) react
with odorants; and, c) to create a pellet with increased nitrogen,
phosphorus or other plant nutrient, e.g., potassium and/or sulfur
such that the treated finished product can be sold profitably into
the commercial marketplace. The advantages associated with the
present invention over the state of the art are numerous and
include any or all of the following: reduction of odors of the
dried pellets, increased nitrogen content in the dried pellet,
increased phosphorus content in the dried pellet, increased iron
content in the dried pellet, increased potassium content in the
dried pellet and/or increased potassium content in the dried pellet
and/or increasing the calcium content or other mineral content in
the dried pellets.
Further, this present invention creates a valuable commercial
agricultural fertilizer as a final product. The product of the
present invention will have significantly more value than the dried
pellets presently manufactured by municipalities or companies under
contract to municipalities to process their biosolids via
heat-drying technologies since heat-dried biosolids pellets contain
only 3% to 6% nitrogen by weight and the present invention teaches
that its product contains 8% to 22% nitrogen by weight. The present
invention describes adding materials such as, preferably,
concentrated phosphoric acid, concentrated sulfuric acid, anhydrous
ammonia, aqueous ammonia, ammonium hydroxide, ammonium sulfate,
ammonium monophosphate, ammonium diphosphate, urea, methylene urea,
sulfur-coated urea, potassium hydroxide, potash, calcium hydroxide,
calcium oxide, attapulgite clay, ferric oxide, ferric sulfate,
magnesium oxide, magnesium sulfate, byproducts such as cement kiln
dust, lime kiln dust, fly ash and wood ash, and combinations
thereof. Also, the present invention teaches that use of
subspecification or substandard preparations of the above
materials, especially the traditional plant fertilizers such as
ammonium phosphates, ammonium sulfates, urea, the slow-release
ureas such as methylene ureas and sulfur-coated ureas, are
desirable and use of such materials enhances the economics of the
processes of the present invention.
The present invention treats the biosolids of a municipal
wastewater treatment plant such that the odorant characteristic of
the biosolids are modified to create a less odorous product upon
heat drying. Further the present invention treats these biosolids
to increase the level of plant nutrients that will be contained and
plant available in the finished heat dried pellet or granule. The
chemical additions are made to the dewatered biosolids in the
typical heat drying plant immediately following the dewatering step
as carried out by belt filter press or centrifuge operations. The
chemical additions are added to the dewatered biosolids by means of
a mixer that blends the additives with the biosolids mix such that
the additives have the opportunity to completely interact and react
with the chemical components of the biosolids. Dewatered, to those
in the art, refers to approximately 8-40% dried biosolids. Dried
biosolids generally refers to above 75%, more preferably above 80%
and most preferably above 90% dried solids.
In one embodiment of the present invention, a concentrated acid or
mixture of concentrated acids, such as phosphoric acid and/or
sulfuric acid is/are introduced to the dewatered biosolids prior to
the drying step in the pellet/granule manufacturing process.
Further, the acid pH created by such acid addition is neutralized
to a pH within the range of pH 4.5 to 7.0, more preferably within
the range of pH 5.0 to pH 6.5, and more preferably within the rang
of pH 5.5 to pH 6.2. Such a preferred desirable pH range is that
preferred by fertilizer distributors and/or the end users, i.e.,
the growers/farmers. The effect of this interaction and reaction is
to lessen the odor associated with the finished heat dried product
and to increase the plant nutrient chemical content and value of
the finished heat dried product.
The present invention describes the addition of concentrated
phosphoric acid, e.g., 70% as super phosphoric acid and/or 50-60%
phosphoric acid (black or agricultural grade phosphoric acid)
directly to the dewatered biosolids after dewatering. The addition
of said phosphoric acid not only reduces the odor associated with
such biosolids but simultaneously increases the phosphorus (P)
content of the finished product. The acid pH which results from
this addition is neutralized by selecting a material from the
group, anhydrous ammonia, aqueous ammonia, ammonium hydroxide,
potassium hydroxide, potash, calcium hydroxide, calcium oxide,
attapulgite clay, ferric oxide, ferric sulfate, magnesium oxide,
magnesium sulfate, and also from byproducts such as cement kiln
dust, lime kiln dust, fly ash and wood ash. Additions of any or
combinations of these simultaneously will increase the
concentration of plant nutrient or soil conditioner in the finished
product and thereby increase the value of the finished product. The
additions of concentrated acids and subsequently of ammonia, either
as aqueous ammonia or anhydrous ammonia or ammonium ions, will have
the dual effect of bringing the mixture pH to a desired range and
will have a disinfecting role in destroying pathogens that are
contained in the dewatered biosolids prior to the drying step of
the pellet/granule manufacturing process.
Further the present invention teaches the use of oxidants such as
ferrate, hydrogen peroxide, ozone and chlorine dioxide in reducing
the odor of said heat dried pellets. Further the present invention
teaches the use of iron oxide and other forms of iron, such as iron
sulfate which can be mixed directly with the dewatered biosolids
and subsequently also react with odorant molecules contained within
the dewatered biosolids thereby resulting in a mix of improved odor
characteristic.
One of the benefits of the present invention is that it utilizes
existing manufacturing operations for the production of the
beneficiated heat dried pellets thereby removing the costly
requirement of constructing such manufacturing plants de novo.
A further benefit of the present invention is that if a
municipality does not want this add-on process to occur within its
own heat-dried biosolid manufacturing plant, the option exists for
the process of the present invention to occur separately following
the production of the traditional heat-dried biosolids pellets by
taking said dried biosolid pellets or granules to a separate
facility. In this separate facility, the heat-dried pellets can be
milled into powder and the present invention then uses said powder
in a process to create a valuable high nitrogen plant
nutrient-containing fertilizer that will compete in the
agricultural wholesale and retail fertilizer marketplace.
The present invention reverses the nature of the product made by
the process as taught in U.S. Pat. Nos. 5,984,992; 6,159,263; and
6,758,879 for manufacturing an organically-enhanced inorganic
fertilizer. The present invention creates an inorganically-enhanced
bioorganic fertilizer by modifying organic-containing heat-dried
biosolids or sludge pellet or granule manufacturing processes. A
preferred example is the modification of conventional heat-dried
municipal biosolids pellets. Such modification permits the addition
of materials into or after the pellet manufacturing process which
add significant plant nutrients to beneficiate or enhance the value
of said pellets in the commercial agricultural fertilizer
marketplace and reduce the odor commonly associated with
traditional heat-dried pellets. In addition, the present invention
teaches a method for treatment of sludges or biosolids to reduce
noxious odorants associated with traditional heat dried biosolids
pellets.
Heat dried pellets of biosolids are often buried or landfilled
because their plant nutrient level and commercial value will not
permit transportation and use in commercial agriculture. Many
others are sold at a price that requires subsidy to support the
transportation costs to bring the pellets from the manufacturing
plant to the end user. The present invention enhances the value of
said pellets and thereby permits and enhances the use of such a
resource as dried municipal biosolids into a mature
marketplace.
Further, the present invention utilizes portions of conventional
methods, such as the AM or Ammonium Melt Fertilizer Manufacturing
Process (see U.S. Provisional Patent Application No. 60/654,957) to
create new and more valuable fertilizers using the heat-dried
biosolids pellet manufacturing process described in the present
invention. Alternatively, the finished heat-dried biosolids pellets
themselves can be used in a separate process independent from the
manufacture of the original heat-dried biosolids pellets.
Municipal wastewater sludge heat-dried pellet production creates a
pellet which has either no or a low value on the commercial
agricultural fertilizer marketplace. This is because of the odors
associated with such products and because of the low plant
nutrients contained in such products. The present invention has the
advantage of the traditional production of heat-dried biosolids in
that it reduces said odors associated with the finished pellets and
simultaneously adds plant nutrients which increase the value of the
finished pellets or granules. It is the teaching of the present
invention that said odor control and plant nutrient enhancement can
be accomplished by adding the same chemical materials, e.g.,
concentrated phosphoric acid (P), aqueous ammonia (N) and or
ferrate solution (Fe).
First Preferred Embodiment
In a preferred embodiment of the present invention, finished
heat-dried biosolids are removed from a municipal wastewater plant
that manufactures said heat-dried biosolids and transports them to
a separate manufacturing plant, preferably as close to the
municipal wastewater treatment plant as possible, for milling and
processing into a high nitrogen containing bioorganic fertilizer.
In this preferred embodiment, milling converts the dry (80% to 100%
solids, preferably 95% to 100% solids, and more preferably 98% to
100% solids) pelletized or granular heat-dried biosolids pellet
into a powder which can then be further processed. As shown in FIG.
1, finished dry heat-dried biosolids pellets or granules are
removed from a typical municipal wastewater treatment plant
biosolids production process and taken to a separate manufacturing
facility for conversion into a plant nutrient rich valuable
fertilizer.
At this separate facility the process is as illustrated in FIG. 2.
Nearly dry or very dry municipal biosolids or organic sludges are
milled into powder and passed into a mixer, most commonly a twin
shafted pugmill that contains plow shaped paddles. This pugmill is
preferably heated by means of an oil-heated jacket or oil-heated
hollow paddles or both. Ferrate, either calcium or sodium or
potassium salt form, is manufactured on site and pumped directly
into the mixer to oxidize any reduced sulfur compounds present in
the powder and to oxidize and react with organic odorants present.
Further the ferrate reacts with the protein content of the powder
and cleaves some of the peptide and amino acid bonds present in the
protein to make smaller monomers which are biologically less
active.
Other odor control agents such as hydrogen peroxide and or chlorine
dioxide or ozone or a combination of these may also be added into
this first mixer. Concentrated phosphoric acid, preferably 54% P
agricultural grade phosphoric acid is next pumped into this mixer
to first neutralize and then acidify the mix and to react with
odorants present in the powder. The mixer creates a thixotrophic
mixture from the dry biosolids powder coupled to the acid and the
odor control agent solution or solutions. This mix is then passed
to a second mixer which may be a pugmill of similar description or
may be a pressure vessel which is capable of receiving a hot mix of
ammonium salts comprised of ammonium phosphate and or ammonium
sulfate. Said second mixer may also be heated by an oil-heated
jacket. Pressures in said second mixer will exceed atmospheric
pressure and may increase in the heated pressure vessel to exceed
10 atmospheres. The preferred pressure will be in the range of 1.5
to 20 atmospheres, more preferably in the range of 3 to 10
atmospheres, and most preferably in the range of 5 to 8
atmospheres. The macromolecular components, especially the
proteins, present in this mix contents of this pressure vessel will
partially hydrolyse and will partially lose their biologic activity
proportional to the time and pressure of their residual time in
said vessel. Further, said chemical and physical heating that
occurs in this second mixer will serve to reduce any pathogens
present to less than the standards of the USEPA's Part 503 rule for
Class A biosolids products. Further, and more preferably, passage
of the mix through this second mixer will sterilize the mix
destroying all viable microorganisms present.
The mix, upon determination of completion of the reactions present
in the second mixer, will be discharged to a third mixer.
Preferably the third mixer is a pugmill, as described earlier. The
purpose of this third mixer is to blend into the fertilizer mix
other plant nutrients as may be required for the manufacture of the
finished fertilizer. One or more of these may be ammonium
hydroxide, ammonium sulfate, ammonium monophosphate, ammonium
diphosphate, urea, methylene urea, sulfur-coated urea, potassium
hydroxide, potash, calcium hydroxide, calcium oxide, attapulgite
clay, ferric oxide, ferric sulfate, magnesium oxide, magnesium
sulfate, and also from byproducts such as cement kiln dust, lime
kiln dust, fly ash and wood ash, or combinations thereof. Further,
this group includes solutions of granulating or hardening agents
such as industrial molasses or lignon or aluminum sulfate to cause
the hardness of the finished fertilizer granule or pellet to be of
agricultural grade hardness, preferably 4 to 10 pounds hardness,
more preferably in the range of 5 to 8 pounds hardness, and most
preferably in the range of 6 to 7 pounds hardness. This third mixer
also contains the capability of having steam and water vapor, which
emit from the mix under the heat conditions present in the mixer,
removed to be later condensed and either placed back into the first
mixer to facilitate the production of a thixotrophic mix or removed
from the process and facility, preferably returned to the municipal
wastewater treatment plant. This removal of moisture from the mix
is crucial to achieving the proper percent solids of the mix for
extrusion, tablet formation or granulation, i.e., the shape-forming
next step in the process.
The mix is discharged to either a granulator or to a extruder or to
a tablet forming machine for shaping into the fertilizer form prior
to drying. Each of these shape forming devices are commercially and
commonly available in the art and each requires a different percent
solids to the mix exiting the third mixer and so it is an important
component of this preferred embodiment of the present invention
that adjustment of the percent solids in this third mixer can take
place in a controlled manner and preferably under automated
computer control.
This shaped fertilizer is then dried to greater than 90% solids and
more preferably to greater than 95% solids and even more preferably
to greater than 97% solids. The dryer is preferably a fluidized bed
apparatus using hot air to dry the shaped fertilizer but it may be
a hot air rotary drum dryer as well. Other drying apparatuses are
also possible in this step such as a vacuum drying apparatus,
preferably a rotary vacuum drying apparatus.
After completion of sufficient drying as described above the
fertilizer is screened to remove oversize material or any fines or
dust associated with the fertilizer. The oversized material is
returned to the input dried biosolids stream and milled and added
to the first mixer in the process. The dust is similarly returned
to the mix and added to the first mixer in the process. By recovery
of said by products there is no waste from this process. Also it
should be clear that when extrusion or tablet making is selected as
the preferred method of shaping the fertilizer there is no need for
the massive equipment associated with granulation requiring ratios
of 4 parts of seed bed to 1 part of incoming mix. Further at times
the recycle ratio may reach 8 parts seed bed to 1 part incoming mix
and therefore requires huge rotating granular machine to
accommodate such granuation technology. Such downsizing affects the
sizing of the manufacturing plant and directly affects the
economics of the manufacturing process.
After the screening the shaped fertilizer is optionally coated with
a commercially available deduster chemical mix in a coating
apparatus. After coating or after screening if no coating then the
fertilizer is cooled in a cooling apparatus and conveyed to a dry
storage facility at ambient conditions. The finished product is
preferably bagged or shipped in bulk.
Second Preferred Embodiment
In a second preferred embodiment of the present invention, nutrient
and odor control chemicals are inserted into the process stream
within the heat-drying plant itself. This is accomplished by
retrofitting existing municipal biosolids heat drying operations or
manufacturing plants. The steps of the second embodiment are
illustrated in FIG. 3. In FIG. 3, equipment supplied for the pellet
beneficiation process are indicated in the solid or green blocks.
The dewatered biosolids are conveyed to a first mixer, preferably a
pugmill, as described in the preferred embodiment. The biosolids
are then treated in this mixer with one or more odor control agents
such as calcium ferrate as described for the preferred embodiment.
The odor treated mix is then acidified in this mixer with
concentrated phosphoric acid in order to control odors and commence
biosolids disinfection and to facilitate production of a
thixotrophic mix in the first mixer or pugmill as also described in
the preferred embodiment. Additional phosphoric and sulfuric acid
is then mixed with the mix. Commercially available aqueous ammonia,
normally 21% N in concentration, is then added to the mixer and
allowed to react with the excess acid present in the mix. Such
reaction results in exothermic heat production facilitating further
mixing and facilitating reaction of the hot ammonium salts with the
organic molecules present in the mix. Further the hot physical
chemical conditions of the mix within this mixer will cause the
partial hydrolysis of some proteins present in the mix from the
heat-dried biosolids that was put in the first step of this
embodiment. Use of aqueous ammonia is also useful in that it is
easier to obtain regulatory permits for its use in and near
municipal wastewater treatment plants further reducing logistics
and liabilities associated with said fertilizer manufacture. This
hot fertilizer mix is discharged to a second mixer such as a
pugmill as described in the preferred embodiment. Additional
required plant nutrients selected from the group described in the
preferred embodiment may then be blended into the fertilizer mix.
Further granulating agents and hardeners may be added to this
mixture to control hardness of the finished granule as described
above. Further, blending of alkaline materials is an option in this
second mixer to create the proper pH of the mix from the acidified
biosolids mixture to produce a resultant mix of pH of between pH
4.5 and pH 7.0. This second mixer is also capable of having water
vapor and or steam removed to produce an viscous material that can
be further processed as required by the shaping mechanism selected,
i.e., similar to the preferred embodiment consisting of extrusion,
tablet formation or granulation. Further processing of this second
embodiment is as described for the preferred embodiment.
In a modification of the second embodiment of the present
invention, anhydrous ammonia is preferably used in a manner as
taught by pending U.S. Utility Patent Application that claims
priority to U.S. Provisional Application No. 60/654,957 as
significant exothermic heat reaction occurs introducing even more
physical heat and pressure as a disinfecting process to the
biosolids prior to their drying step in the manufacture of high
nitrogen containing pellets or granules.
Third Preferred Embodiment
The third preferred embodiment describes adding to the sludges or
biosolids within a wastewater treatment plant manufacturing
heat-dried biosolids as illustrated in FIG. 4, odor control agents
such as ferrate or hydrogen peroxide followed by adding to the
biosolids, nutrient materials, preferably, solid fertilizers,
ammonium sulfate, ammonium nitrate, mono-ammonium phosphate,
di-ammonium phosphate, potash, urea and combinations thereof.
Further, this embodiment teaches liquid fertilizers, such as urea
ammonium nitrate ("UAN"), are mixed with the biosolids prior to
drying and liquid fertilizer. Finally, materials may be added to
the mix selected from the group, ammonium hydroxide, potassium
hydroxide, potash, calcium hydroxide, calcium oxide, attapulgite
clay, ferric oxide, such as ferrate, ferric sulfate, magnesium
oxide, magnesium sulfate, and also from byproducts such as cement
kiln dust, lime kiln dust, fly ash and wood ash. This embodiment is
a simple odor control and nutrient enrichment of the biosolids
prior to being dried by the mechanisms already present in the
heat-dried biosolids production system used by the municipal
wastewater treatment plant. This is as much as a non intrusive
addition of materials within the wastewater treatment plant as is
possible and still produce the desired nutrient enhanced valuable
product.
Fourth Preferred Embodiment
A process of fertilizer manufacture accomplished by modifying
existing or to be built organic heat drying operations or
manufacturing plants to cause the manufacture of a beneficiated
dried organic pellet or granule that has an inorganic plant
nutrient value sufficient to be competitive on the commercial
agricultural marketplace comprising: Acidifying dewatered biosolids
prior to drying with concentrated phosphoric acid in order to
control odors and commence biosolids disinfection; Producing a
blended thixotrophic mix of the dewatered biosolids with the
concentrated acid; Blending conditioners and hardeners to this
mixture to control hardness of the finished granule; Blending
ammonia with the blended mix of acid with dewatered biosolids;
Blending plant nutrients with the blended mix of acid, ammonia and
dewatered biosolids; Removing water from the mixture as steam and
water vapor to produce an viscous material that can be further
processed; Creating a soil-like material or pellets or granules
from said mixture; Drying said material to greater than 90% solids;
Cooling said dry material; and, Storing said dry material in a dry
environment protected from the weather until transported for use as
fertilizer.
The following examples illustrate embodiments of the invention, but
should not be viewed as limiting the scope of the invention.
EXAMPLES
Example 1
This example describes the approach of chemically and biologically
modifying the dewatered biosolids prior to drying such that the
odor of the pellet product is significantly improved. Dewatered
biosolids are preferably above 8% solids, more preferably above 15%
solids, more preferably above 25% solids, and most preferably
approximately 40% solids. This exemplary embodiment also creates
added value to the pellet product for sale into the fertilizer
market for commercial agriculture.
The illustration of this Example can be found in FIG. 5. This is a
more detailed description of the first embodiment of the present
invention. The process employs three pugmills in sequence to
accomplish the production of the beneficiated heat-dried pellets.
Heat-dried biosolids are received into an augured hopper (1). This
is sized to accept up to one full 20 ton container of dried
biosolids. The live bottom bin contains one or more augers (2) that
move the pellets to a mill (3) which pulverized the pellets into a
powder. The powder leaves the mill at a defined rate (4) to the
first mixer (17) where the powder is conditioned and prepared for
later mixing with a hot melt of ammonium salts. This mixer is
optimally a pugmill configured with double shafts that may be
hollow to accept heated oil which will begin the process of heating
the biosolids. Alternatively, heat may be applied through a jacket
configuration around the pugmill with heated oil (23) supplied by
an oil heater (50).
Pugmill #1 (17) has on its anterior end an injection ring (18)
which permits the addition of liquid materials to the powder also
entering the pugmill. There are several additions that may be made
to the heat-dried biosolids powder in pugmill #1. The first of
these are the additives for odor control that are added to the
powder to control or eliminate the traditional musky nitrogenous
odor of dried biosolids. Dependent upon the concentration of the
ferrate, some process water (118) may be added into this pugmill #1
to assist in creating a thixotrophic paste for the ferrate and
other odor control agents to react with. Ferrate (sodium or
calcium) (6), a liquid is added as a very strong oxidant to control
reduced sulfur compound and nitrogenous odors present in the
biosolids. The calcium (or sodium) ferrate is added from apparatus
(6) at rate (15) through control of a pump (14). This oxidative
agent is very effective at destroying the odorants present in the
mix when used at 1 to 10 percent and preferably at 2 to 5 percent
of the volume of wet powdered biosolids contained in the pugmill #1
contained at an estimated concentration of 55% solids. The ferrate
is known to react very effectively with reduced sulfur compounds
present in the mix. It also is a strong enough oxidant to actually
denature proteins and is even capable of disrupting the bonds
between amino acids. Such denaturing of proteins and disruption of
molecular bonds can alter the odorant characteristics of the
biosolids mix thereby improving the odor of the resultant product
of the invention. Additionally, two other oxidative materials may
be added in this embodiment. Liquid hydrogen peroxide (7) at 25 to
50% concentration is added by control of pump 19 at rate 20,
between 1% and 5% of the biosolids delivery rate 16 to injection
ring 18 into pugmill #1 (17). Optionally, calcium hypochlorite (8),
a solid, may be delivered by screw conveyor 21 to a pulverizing
mill 29 and then to an additive port (30) at a rate (25) equal to
between 1% and 5% of the volume of powdered biosolids (4) contained
the pugmill #1 at an estimated concentration of 55% solids. Use of
the mill is important in optimizing these solids materials for
contact with the odorant molecules present in the biosolids.
Addition of phosphoric acid (5) via pump 12 at rate 13 acidifies
the organics present in the biosolids and significantly assists in
the odor control of the mix (and the final product) resulting in
less sulfides being liberated throughout processing and less
reduced sulfur compound odor, e.g., hydrogen sulfide or mercaptan,
being detectable in the finished product. Acidic conditioning of
the mix is useful in processing the powdered biosolids for several
reasons. Additionally, the addition of phosphoric acid helps to
prevent oxidative heating of the finished product when this product
is stored statically for long periods of time (see U.S. Patent
Application No. 60/654,957). Also it is important to note that this
phosphoric acid (5), as well as the iron added in the ferrate (6)
and the iron oxide, also known as magnetite (Fe3O4) (9) contribute
important plant nutrients to the fertilizer mix. The liquid acid is
added to the mix through insertion ring 18 into pugmill #1 (17). It
should be noted that the addition of acid in this step could be
with the use of concentrated sulfuric acid although this acid tends
to create additional reduced sulfur compounds like hydrogen sulfide
or mercaptans during processing some of which can end up in the
finished product and create problem odors.
As the milled dry biosolids enter mixer or pugmill #1 (17) at rate
4 they are aggressively mixed and converted to a thixotrophic
paste-like material that easily reacts with the odor control
agents, the acid and any process water (118) also added into
pugmill #1. This pugmill is long enough and has sufficient
retention time to accomplish this conversion. This pugmill has a
horizontal mixing chamber with plow-shaped blending paddles mounted
on two powerfully driven shafts that rotate at a speed which
divides, mixes, back-mixes and re-divides the materials to be mixed
to yield a thorough, uniform blend with reliable consistency. This
and the other plow-blending pugmills used in the processing
sequence are independently heated by means of a jacketed sleeve
around the apparatus. Such heating is adjustable to provide a
heated paste prior to blending with the hot ammonium salt. Such
heating is also applied to the plow blending apparatus carrying out
the mixing of the hot ammonium salt with the thixotrophic paste of
conditioned mix.
The mix exiting this initial pugmill #1 should have achieved the
temperature of 95 F. Establishment of higher than ambient
temperatures in the bioorganic mix facilitates its later homogenous
blending with the hot melt of ammonium salts and ensures that the
heat energy contained in the ammonium salts is advantageously used
to sterilize the mix. Further, the preheating of the thixotrophic
or plastic bioorganic paste permits sufficient heat in the mix to
occur in the second pugmill such that partial denaturation of
proteins and partial hydrolysis of organic molecules that were
contained in the input bioorganic material will be facilitated.
The bioorganic mix exits pugmill #1 at rate 33 and enters an
elongated pugmill (119). The biosolids mix moves into pugmill #2 at
rate 33. The pugmill #2 is heated with hot oil (23) passing through
a jacket around outside of the vessel. Simultaneously with the
addition of the conditioned mix, a liquid hot or molten ammonium
salt mixture enters the pugmill at rate 34. The ammonium salt
mixture is manufactured in a reactor (32) by combination of
concentrated sulfuric acid (10) and or phosphoric acid (5) with
aqueous ammonia (11) at 21% N in nitrogen concentration. The
sulfuric acid (10) is added with phosphoric acid (5) at rates 28
via pump 23, and 27 via pump 24 respectively, such that the amount
of ammonium sulfate and ammonium phosphate created when mixed with
the conditioned mix produces a high nitrogen fertilizer, i.e., a
15% nitrogen by weight in the final fertilizer product. Further
this combination of sulfuric acid and phosphoric acid is controlled
such that a small amount of acid is in excess of the amount of
ammonia also added to the reactor. The finished ammonium salt mix
has an exit pH of approximately pH 6.0. The size of the reactor is
set such that sufficient resident time occurs for the reaction
between the acids and the ammonia to go to completion. The reaction
between the acids and the ammonia is violently exothermic. The
reaction creates high heat which maintains the resultant ammonium
salt in the soluble molten state with any water present in the form
of superheated steam. This violent exothermic reaction also will
create significant pressure within the reactor vessel. This
ammonium salt mix has a temperature characteristic that is greater
than 295 F.
If anhydrous ammonia were to be used in place of the aqueous
ammonia the temperature will be significantly higher reaching
temperatures in excess of 400 F. The temperature of the ammonium
salt is such that when it is blended with the conditioned mix in
the pugmill #2 the temperature of the blend exceeds 255 F via the
combination of the heat from the ammonium melt and the heat
provided via the hot oil jacket around the pugmill. The higher the
temperature the more denaturization and hydrolysis of proteins and
peptides in the organic mix will occur, especially in the acid
environment of the interior of the pugmill. The partial denaturing
and hydrolysis of the organic molecules in the organic mix creates
advantageous properties in the final fertilizer product that result
in increased crop production compared to fertilizers that do not
contain such organic material, i.e., ammonium sulfate or ammonium
phosphate or urea fertilizers.
The pugmill holds hot fertilizer mix for approximately 3 minutes in
this apparatus. This time must be greater than 60 seconds and
preferably about 5 minutes. During the resident time in pugmill #2
(17) the paddle blades are continually mixing the contents of the
pugmill which because of the exothermic reaction occurring will be
under some increased pressure. The pugmill #2 may be inclined
upward to permit increased pressure within the vessel.
The fertilizer mix exits the pugmill #2 at rate 55 and enters
pugmill #3 (120). In pugmill #3 various materials are added to
bring the nutrient concentration of the finished product up to the
required specification, to increase the hardness and granularity of
the finished product and to adjust the pH of the mix to the correct
pH as required by the specification of the finished fertilizer
product.
The solid nutrients that may be added include urea, ammonium
nitrate, mono-ammonium phosphate, diammonium phosphate (57), and or
potash (KCL) (58). The solids used to adjust the pH are principally
alkaline agents (59) selected from the group comprised of calcium
carbonate, sodium hydroxide, calcium oxide, cement kiln dust, lime
kiln dust, Class C fly ash, Class F fly ash, multistage burner ash,
alum, alum sludge from water treatment and wood ash. Ferric oxide,
in this example, it is magnetite (Fe3O4), may be added here for
odor control of the mix and final fertilizer product and for iron
content in the finished product for agronomic reasons. These solid
materials are added via screw conveyors (66, 68, 70 and 22) at
specific rates for each compound, diammonium or mono ammonium
phosphate (67), potash (69) and the alkaline agent at rate 71 and
the ferric oxide (9) at rate 26. These solids are conveyed to a
pulverizing mill (72) to increase the efficiency of blending and
reaction with the fertilizer mix entering the pugmill 120 from the
pressure vessels. The powder is then transported via a screw
conveyor at combined rate 73 to enter the pugmill 120. In this
example only magnetite (Fe3O4) (9) is added to pugmill #3 to bring
the iron content to 2% in the final fertilizer product.
Liquid additives preferably include nutrients such as UAN (urea
ammonium nitrate) and soluble urea (both not shown in FIG. 3). The
liquid additions also include pH adjustment materials (54) such as
acids, e.g., phosphoric acid or sulfuric acid, or caustic
solutions, e.g., sodium hydroxide. These are pumped (60, 62, and
64) are respective rates (61, 63, and 65) to enter pugmill #3
(120).
The pugmill #3 is preferably jacketed to heat the fertilizer mix
within to prepare the mix for injection into the shaping mechanism.
The heat is applied through a jacketed chamber around the pugmill
heated with hot oil 41. Exhausted oil is returned to the oil heater
through pipes 35 from pugmill #3 and pugmills #1 (17) and pugmill
#2 (119).
Pugmill #3 is long enough and has sufficient retention time and
agitation via the double shafted plow blending paddles to blend the
additives with the fertilizer mix and insure the retention of
sufficient heat to achieve effective shaping.
Shaping may occur by use of a traditional granulator containing a
heated seed bed or it may occur by extrusion technology or
innovatively by tablet formation as used in the pharmaceutical
industry.
In this example the discharge from pugmill #3 is screw conveyed at
rate 75 to an extruder machine (76) that contains dies permitting a
3 mm diameter extrusion of the mix. A high speed air cutter cleaves
the extrusion to a arrange of 3 mm to 3.5 mm. The temperature of
the mix in this example was 225 F but it should be in the range of
212 F to 350 F and preferably in the range from 250 F to 300 F.
Further the percent solids of the fertilizer mix can be controlled
by the withdrawal of steam and water vapor via (53) from pugmill #3
and from the extruder (76). The computer controlled removal of
water is such that the fertilizer mix is the correct solids for
shaping. The percent solids of the mix in this example was 74% but
it should be in the range from 40% to 85% with the preferred range
from 50% to 80% and the more preferred range from 60% to 75%.
The retention time in the shaping apparatus is not critical to the
process but will range between 30 seconds and 15 minutes. In this
example it was about 1.1 minutes.
Pelletized fertilizer mix exits the extruder 76 at a percent solids
range of about 88% but should range from 80% to 94% and preferably
in the range of 85% to 94%. The temperature of the exiting mix is
195 F but should range between 185 F and 225 F although this range
is not critical for operation of the fluidized bed dryer (88) or
rotary drum (not shown in FIG. 5) dryer. The retention time in the
dryer is between 3 and 25 minutes depending upon the design and
size of the dryer. The dryer illustrated in FIG. 5 is a vertical
fluidized bed dryer which operates by keeping the drying fertilizer
granules in suspension while hot air passed upward past them
removing water and increasing dryness to the specified level. The
time in the dryer in this example was about 9 minutes. The product
in this example achieved 97% dryness; however, the range of dryness
of the product should range from 90% to 100% with the preferred
range from 96% to 99%.
Dry, pelletized fertilizer is then passed (87) to the screen system
(81) where the specification size is removed at rate 91 for coating
with hot oil. The specification size may be varied dependent upon
customer requirements, however, the range of suitable product for
sale is between 0.7 mm and 3.2 mm with the commercial range for
normal sized fertilizer is between 2 mm and 4 mm. The present
invention also can manufacture a minimal sized product suitable for
use in golf course applications which ranges from 0.7 mm to 1.3
mm.
Any undersized material after shaping is directly conveyed back to
the pugmill #3 at rate 86. Any oversized material is conveyed to
hammer mill or mill 82 where it is pulverized 83 and returned to
either the pugmill #3 via common conveyor 86.
The specification fertilizer product is conveyed to a oil coating
apparatus, e.g., a coating drum (93) in this example. The coating
oil or material is contained in a container (92) that must be
heated in this example to about 180 F to keep it fluid for
application. The coated pellets which are still hot then pass to a
cooler apparatus, e.g., air blown cooler (96) for reduction in
temperature to less than 130.degree. F. in this example.
Following cooling the finished product is weighed (not shown in
FIG. 3) and conveyed (97) to dry storage pending bagging and or
bulk shipment.
The process air from the pugmill #3 (53), extruder (90), fluidized
bed dryer, the screens, mill, oil coating drum and air pellet
cooler is ducted to the bag house (102) to be filtered while still
hot enough to carry the removed water as vapor. The cleaned air is
passed to a condenser (104) where the air is cooled with clean
water sufficiently that the water vapor is converted to liquid
which is piped to pugmill #1 to create a thixotrophic paste from
the powdered biosolids or removed from the process to a sewer or
water treatment system prior to discharge to the environment. The
process air following condensation is passed to an acid (105) and
caustic (106) scrubber for odorant removal prior to its passing to
a biotrickling filter (111) for final removal of all odorants. This
unit employs a medium with microorganisms using clean water and
process water (not shown in FIG. 5) mixed with the proper nutrient
at rate to wet the medium and feed the microorganisms. Air may be
recycled to provide sufficient retention time until odors are
removed prior to discharge (116) to an exhaust fan (117) for
discharge to the environment.
Example 2
This example describes the approach of modifying the production of
heat-dried biosolids within a municipally operated wastewater
treatment plant. The plant produced dewatered biosolids a
chemically modified prior to drying such that plant nutrient
chemicals and odor control agents are added such that the final
pellet product is significantly improved as a fertilizer so that it
can be sold into the fertilizer market for commercial
agriculture.
This example results in full scale operation of a municipal
wastewater treatment plant producing beneficiated heat dried
biosolids pellets or granules. Because some of the additives
contain plant nutrients such as nitrogen, phosphorus and other
plant nutrients such as potassium and or sulfur, the fertilizer
value of the pellet will be increased. The pellets that are
anticipated as a product of the improved processing scheme (the
present invention) are referred to as inorganically-augmented
bioorganic fertilizer. There is an increasing need for
organically-based fertilizers in the U.S. and worldwide
agricultural marketplace. After years and years of repetitive
inorganic fertilizer application the soils of farms, especially
commercial farms are in desperate need of organic content to
maintain expected (and now economically required) crop production
rates.
Many cities have been in the business of producing a high quality
heat-dried pellet from their biosolids following belt filter
pressing or centrifuge dewatering procedures. Unfortunately these
pellets often have a detrimental odor associated with them which
has very adversely affected the ability of municipality to market
these into the agricultural community. Often the cities are forced
to mix their dried pellets with soil and bury them in a landfill.
The traditional pellet manufacturing system provides little or no
recovery of costs associated with production of the heat-dried
biosolids or their eventual disposition. Early in the history of
production of heat dried biosolids pellets or granules the market
for the sale of non-beneficiated dried pellets or granules was
sufficient to cause them to be transported to farms for their
application as a low grade fertilizer or soil conditioner. When
larger numbers of municipal heat drying pellet producing operations
when on line then the supply of this fertilizer outstripped its
commercial marketplace and the price fell to a level that requires
subsidy payments by the municipality to ensure timely removal and
disposition of the finished pellets. This example for the present
invention creates a product that has sufficient characteristics and
plant nutrients to command a suitable price to permit its timely
transport and sale into the commercial agricultural fertilizer
marketplace.
There are a number of chemical additions to the city's biosolids.
The types of additives planned are: 1) acids but with the finished
pellet pH meeting fertilizer requirements; 2) oxidants for odor
control; and 3) specific binder materials to create harder finished
pellet products to meet agricultural specifications for
hardness.
This example also utilized the addition of iron oxide will have a
positive effect on the odor of the finished dry pellets. The use of
this material introduces a wide prospect of differing chemical and
physical forms and grades of this material. Again, similar to
additions of nitrogen and phosphorus, the addition of iron will
beneficiate the plant nutrient value of the enhanced city's
finished pellet.
The action or input locations where modifications to the existing
municipal heat drying biosolids process to beneficiate the pellet
product are shown in FIG. 1 in Notes #1 and #2. The majority of
chemical additions will be at one or two pug mills placed into the
municipality's process scheme and which are located after the
dewatering of the material by centrifuge (see #2 in FIG. 1). The
various additives which are described below are added here and
blended into the dewatered biosolids.
It is very important to evaluate the potential value of the
augmented dried pellets that are created. It is a goal that the
commercial value of the pellets be beneficiated or enhanced so that
they can be competitively sold into the fertilizer marketplace.
This will remove the negative costs associated with the present
practice of mixing dried pellets with soil and burying them in a
landfill. Instead, the beneficiated pellets will be sold for
significant positive value because the augmentation strategy will
create a high value if implemented on a full scale by the
municipality. An average chemical plant nutrient quality of a
municipal dried biosolids pellets has an N content of 2 to 5
percent, but can be made significantly more valuable by increasing
the N components. The nitrogen content will be increased to 12
percent nitrogen (N), 8 percent phosphorus (P as in P.sub.2O.sub.5)
and 2% iron (Fe). No potash is added in this example so that a
12-8-0 (N-P-K) fertilizer was manufactured. Such a product creates
positive product value for the municipality and removes the
negative value presently associated with this product.
FIG. 6 shows the details of the additive chemicals used in this
example. The dewatered biosolids was produced as before the present
invention is introduced in to the process scheme. To accomplish the
chemical additions it is preferred that two pug mills are inserted
into the conveying system after the dewatering step and prior to
the shaping of the material and its drying to pellets or granules.
Both liquid and solid additions are made to pugmill #1 (11).
Initially, as in Example 1, ferrate is manufactured on site and is
pumped from its storage container (3) via pump 5 at rate 6 to the
pugmill #1. Ferrate is a strong oxidant and rapidly reacts with
reduced sulfur compounds and also reacts with proteins as described
earlier. Second, a strong acid, preferably phosphate acid is pumped
(4) at a rate (8) to the pugmill at orifice (9) for mixing as well.
This acid helps in producing a thixotrophic mix from the dewatered
biosolids and helps with the odor control process. Other odor
control agents, hydrogen peroxide and calcium hypochlorite can be
used in the present invention but were not used in this
example.
The pugmill #1 is configured as a double shafted plow bladed
pugmill. The mix passing through this pugmill is thoroughly mixed
and is a thixotrophic paste as it is discharged to pugmill #2 (20).
Pugmill #2 receives plant nutrients from containers housed at the
wastewater treatment plant. The solids are milled (31) prior to
being introduced to an orifice in the pugmill. In this example,
urea (22) is added via screw conveyor (25) at a controlled rate
(28) to the mill (31). Similarly, magnetite, Fe.sub.3O.sub.4, (23)
is also added as a nutrient and as an odor control agent through
conveyor (27) to the mill (31) for delivery to the pugmill and
mixing with the conditioned biosolids. Also, in this example, a
granulating agent (14), lignon, via pump 16 was also added at rate
18 to assist in the hardening of the finished dry granule. Upon
discharge from the pugmill #2 the fertilizer mix reenters at rate
(33) the processing train (34) of the municipal wastewater
treatment plant and is shaped and dried into pellets or granules
(36) and discharged at a rate (35). The finished product in this
example, as a 12-8-0 fertilizer can be marketed as a commodity
agricultural fertilizer.
Other embodiments and uses of the invention will be apparent to
those skilled in the art from consideration of the specification
and practice of the invention disclosed herein. All references
cited herein, including all publications, U.S. and foreign patents
and patent applications, and materials of any kind which are cited
to herein, are specifically and entirely incorporated by reference.
It is intended that the specification and examples be considered
exemplary only.
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